Printed circuit substrate with resistance elements

ABSTRACT

In a printed circuit substrate incorporating a resistor pattern film and a conductor pattern film are formed on the two surfaces of a high conductive material layer such as a copper foil, respectively, in a predetermined positional relationship, and an insulating support is combined directly or indirectly with the resistor pattern film on the high conductive material layer, whereby a printed circuit board with resistance elements having high performance can be manufactured, while the number of processing steps can be greatly reduced.

BACKGROUND OF THE INVENTION

This invention relates to printed circuit substrates incorporatingresistance elements, and more particularly to a novel printed circuitsubstrate with resistance elements in which a resistor pattern film anda conductor (including electrodes) pattern film are incorporated inadvance, whereby a printed resistor circuit board with resistanceelements having high performance can be manufactured, while the numberof processing steps can be greatly reduced.

A conventional printed circuit substrate incorporating a resistor, whichis well known in the art, is a multilayer stock comprising an insulatingsupport, a resistance layer combined with the entire surface of theinsulating support, and a high conductive material layer combined withthe resistance layer. In the case where a printed circuit board withresistors is fabricated by using this conventional printed circuitsubstrate, an insulating region (all the layers on the insulatingsupport being removed), a resistance region (the high conductivematerial layer being removed), and a conductor region (none of thelayers being removed) are formed by a subtractive method (mask-etchingmethod).

A typical one of the prior art concerning printed circuit substrates ofthis type is that disclosed by Japanese Patent Laid-Open No. 73762/1973.According to this publication, a printed circuit substrate ismanufactured and converted into a printed circuit board with resistorsthrough a number of intricate processes as outlined below: One surfaceof a high conductive material layer such as a copper foil is coveredwith a removable masking sheet, and a resistance layer is formed on theother surface of the high conductive marterial layer byelectrodeposition. Then, the masking sheet is removed, and thereafter aninsulating support is combined with the resistance layer. Thus, theprinted circuit substrate incorporating a resistor is obtained.

This substrate is further subjected to the following processes: Afterthe surface of the copper foil of the substrate is covered withphotoresist, it is subjected to exposure through a photographic negativehaving a conductor pattern and a resistor pattern in combination (havingtwo patterns corresponding to the conductor region and the resistorregion) and is then subjected to development, whereby the photoresist ismantained unremoved in the pattern regions. The copper foil in theregion which is not covered with the photoresist is removed by etching,and furthermore the resistance layer exposed is removed by using anetching solution, as a result of which the surface of the insulatingsupport is exposed. Then, the left photoresist is removed by using aremoving solution.

Thereafter, the substrate is covered with photoresist again, and is thensubjected to exposure through photohgraphic negative having theconductor pattern. The substrate is subjected to development to retainthe photoresist in the conductor pattern region. The copper foil in theregion which is not covered by the photoresist (or the copper foilhaving a configuration corresponding to the resistor pattern region) isremoved by etching, as a result of which the surface of the resistancelayer corresponding to the resistor pattern region is exposed. Then, theremaning photoresist is removed by using a removing solution.

A solder stop-off or the like is applied to the resistance layer in theresistor pattern region by printing, and is then heated and cured tocover the resistance layer. Thus, the printed circuit board withresistors is obtained.

However, the drawback in the above-described process is that, in thesecond process of cleaning and removing the remaining resist (on theconductor pattern region) by using the removing solution, the resistancelayer in the resistance pattern region has been exposed already and issubject to the removing solution. The thickness of the resistance layeris made to the considerably thin, of the order of several hundreds tothousands of A, in order to increase its sheet resistance. Accordingly,its mechanical strength is very low. Especially, if it is rubbed in aresist removing solution, its combining force with the combining surfaceof the insulating support is reduced, which leads to damage, theinsulating support being, in general, a laminated plate of epoxy resinand glass cloth. Thus, variation of the sheet resistance and lowering ofa variety of characteristics are caused.

In order to overcome these various difficulties, a method has beenproposed in which the conductor pattern region of the circuit substrateis protected by a gold plating film, and in the final process the copperfoil having a configuration corresponding to the resistor pattern regionis removed by etching. However, persons skilled in the art will readilyunderstand that in this method the processes are rather intricate,requiring considerable skill.

As is apparent from the above description, the conventional printedcircuit substrate incorporating a resistor and its processing techniquesuffer from various disadvantages that, because the number of processingsteps is relatively many and the processes are intricate, it takes arelatively long period of time for the processing, the manufacturingcost is high, the yeild is limited to a certain extent, and theauxiliary material cost is high.

Accordingly, the printed circuit substrate of this type cannot beextensively employed in a variety of industrial fields without solvingthe above-described problems accompanying the conventional printedcircuit substrate.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of this invention to eliminate allof the above-described difficulties accompanying a conventional printedcircuit substrate incorporating a resistor.

More specifically, an object of the invention is to provide a printedcircuit substrate incorporating resistance elements in which the numberof manufacturing steps is reduced when compared with that in the case ofthe conventional one.

Another object of the invention is to provide a printed circuitsubstrate incorporating resistance elements in which an anti-corrosivemetallic material can be employed as its resistor pattern film therebyimproving the stability and performance thereof.

A further object of the invention is to provide a printed circuitsubstrate incorporating resistance elements in which two or moreresistor pattern films different in sheet resistance are incorporatedtherein and the resistance range of its resistance elements can beincreased.

A still further object of the invention is to provide a printed circuitsubstrate incorporating resistance elements in which the manufacturingcost is reduced and the amount of material is also reduced when comparedwith those in the case of the conventional one.

The foregoing objects and other objects of the invention have beenachieved by the provision of a printed circuit substrate with resistanceelements which, according to this invention, comprises a high conductivematerial layer, and an insulating support, the high conductive materiallayer having a resistor pattern film and a conductor pattern filmrespectively on both surfaces thereof in predetermined positionalrelation to each other, the high conductive material layer beingcombined with at least one surface of the insulating support through theresistor pattern film.

In this invention, it is necessary that the resistor pattern film andthe conductor pattern film provided respectively on the two surfaces ofthe high conductive material layer are arranged in a predeterminedpositional relation to each other. The term "predetermined positionalrelation" is intended to mean a positional relation in which apredetermined printed circuit board with resistance elements can beobtained by processing the printed circuit substrate.

In the invention, an anti-corrosive material which is not affected by anetching solution for etching the high conductive material layer isemployed as the conductor pattern film, so that the printed circuitboard with resistance elements can be obtained by etching the highconductive material layer only once (if necessary, the resistor patternfilm being covered with a solder stop off), which leads to a reductionof the number of processing steps. Furthermore, as the material of theresistor pattern film, an anti-corrosive metallic material is preferablyemployed which is not affected by one application of the etchingsolution for etching the high conductive material layer. In this case,in view of the strength and accuracy of the resistance element, it ispreferable to form the resistor pattern film with an anti-corrosivemetallic material by plating which is not affected by the etchingsolution and which is equal to or different from the material of theconductor pattern film, to the thickness of the order of 100 A to 2000A. The resistor pattern film may be also formed by printing according tothe ordinary method.

The nature, principle and utility of the invention will become moreapparent from the following detailed description and the appended claimswhen read in conjunction with the accompanying drawings, in which likeparts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1 through 4 are diagrams of a description of steps ofmanufacturing a printed circuit substrate with resistance elementsaccording to this invention. More specifically, the parts A of FIGS. 1through 4 are plan views showing the printed circuit substrate beingmanufactured, while the parts B of FIGS. 1 through 4 are sectional viewstaken along lines I--I' in the parts A of FIGS. 1 and 4, respectively.

FIG. 5 and FIG. 6 are diagrams for a description of steps of convertingthe printed circuit substrate into a printed circuit board. Morespecifically, the parts A of FIGS. 5 and 6 are plan views showing theprinted circuit substrate being processed, while the parts B of FIGS. 5and 6 are sectional views taken along lines I--I' in the parts A ofFIGS. 5 and 6, respectively; and

FIG. 7 is an explanatory diagram illustrating an operation for providingin a predetermined positional relationship a resistor pattern film and aconductor pattern film on a high conductive material layer in theprinted circuit substrate according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

One preferred example of a printed circuit substrate according to thisinvention will be described in detail with reference to the accompanyingdrawings.

A photoresist is applied to both surfaces of a high conductive materiallayer 1 such as a copper foil with a dip coater or a roll coater, and isthen subjected to drying, thereby forming photoresist layers 2 and 2' onthe two surfaces of the copper foil as shown in the parts A and B ofFIG. 1.

Then, one side of a photographic negative 11 for forming a conductor(including electrodes) pattern is connected, in the form of a hinge, toone side of a photographic negative 12 for forming a resistor pattern bymeans of a clip 13 or the like, as shown in FIG. 7. Thereafter, thecopper foil coated with the photo-resist is placed between the twophotographic negatives 11 and 12 and is subjected to exposure by the useof a double surface exposor. The copper foil with the photoresist layersthus treated is developed whereby the surfaces of the coppercorresponding to the conductor pattern and resistor pattern regions areexposed as shown in FIG. 2.

The two pattern regions on the copper foil are plated, so that aconductor pattern film 3 and a resistor pattern film 4 are formed on twosurfaces of the copper foil 1, respectively, as shown in FIG. 3. Withrespect to the composition of the plated film, if a metallic materialstable with an etching solution for copper corrosion carried out lateris employed, the plated film in the conductor pattern serves asetch-resist during etching the copper. However, in the case where ametallic material which is not so stable with the etching solution forcopper corrosion is employed, after plating as resistor pattern film(resistance elements) and conductor pattern film has been carried out inthe two pattern regions, the conductor pattern film can be additionallyplated with an anti-corrosive metal while resistor pattern film beingmasked.

Then, after the photoresist layers and the masking agent left after theplating process have been removed, the unit is subjected to washing anddrying. Thereafter a glass cloth impregnated with epoxy resin (so-calledprepreg), for instance, is placed on the side of the unit where theresistor pattern is provided, and is then heated and pressurized,thereby forming an insulating support 5 as shown in FIG. 4. Thus, aprinted circuit substrate with resistance elements in which the resistorpattern film is incorporated and the conductor pattern region is formedby the anti-corrosive conductor pattern film, has been fabricated.

With the printed circuit substrate according to this invention, aprinted circuit board can be manufactured by a simple process includinga copper etching operation. More specifically, the printed circuitsubstrate shown in FIG. 4 is immersed into an etching solution forcopper corrosion, as a result of which the exposed portions of thecopper foil 1 are subjected to etching and therefore the insulatingsupport 5 is exposed. In this case, the conductor pattern film 3 and theresistor pattern film 4 are not corroded by the etching solution. Aftercompletion of the etching process, the unit is subjected to washing anddrying, as a result of which the printed circuit board shown in FIG. 5can be obtained. If necessary, a cover coat layer 6 may be applied onthe surface of the unit for the protection of the resistor pattern film4 as shown in FIG. 6.

The above description is to outline the invention. The materials ofcomponents suitable for embodying the fundamental concept of theinvention, and the structural improvement and modification included inthe invention will now be described more concretely.

A copper foil is most extensively employed as the high conductivematerial (layer) used in this invention; however, an aluminum foil, atin-plated copper foil, an zinc foil, and a silver foil can be employedalso.

With respect to the conductor pattern film formed on the high conductivematerial layer, it is preferably formed with a metallic material havinga sufficiently high corrosion resistance against an etching solution byelectroplating or chemical plating, because as is apparent from thestructure of the unit according to the invention the period of timeduring which the conductor pattern film is in contact with the etchingsolution is longer than the period of time during which the resistorpattern film is in contact with the etching solution. The resistorpattern film can be formed by utilizing a metallic material, and may bea plated film of metallic material which is equal to or different fromthe conductor pattern film in material quality. Therefore, noble metalssuch as gold, slver, platinum and rhodium or alloys of them,anti-corrosive metals such as tantalum, tungsten, titanium, molybdenumand chromium or alloys of them, and tin-cobalt, tin-zinc, tin-cadmium,nickel-phosphorus alloys which are improved in corrosion resistance byalloying, can be employed as the materials of the two films.Furthermore, it is preferable to determine the metallic material bytaking into consideration not only the corrosion resistance but also itselectrical characteristics such as resistance, temperature coefficient,and resistance stability; its mechanical characteristics such assoldering characteristics and sliding characteristic as a conductor orelectrode; and the characteristics of a plating bath such as throwingpower, and stability of a bath which may greatly affect the yield in aplating process. In view of the foregoing, the plating of tin-nickelalloy is one of the kinds of plating which is preferred on the basis ofstability in alloy composition and cost.

On the other hand, in the case where the plated film of a metallicmaterial is limited to a material or a thin film which is excellent incharacteristic as the resistor pattern film but is inferior in corrosionresistance as the conductor pattern film plating may be carried outadditionally to cover the conductor pattern film with a metallicmaterial which is different in quality from the resistor pattern filmand is high in corrosion resistance, or a conductor pattern film may beformed with the different metallic material which is the same as theabove-mentioned additionally covered material.

Furthermore, in the present invention, it is possible that a resistorpaste obtained by mixing a fine powder of carbon such as lamp black,graphite or the like with a binder such as methacrylic resin, epoxyresin or the like is printed on a high conductive material layer byscreen printing and is then cured at a temperature of the order of 140°to 180° C. to obtain resistor pattern film in a desired shape.

Employed as the insulating support are laminated plates made of epoxyresin - glass cloth, polyester - glass cloth, polyimide - glass cloth,polyamidomide - glass cloth, phenol resin - paper, and epoxy resin -paper; polyimide; polyester; polyamidoimide; and a flexible insulatingsheet or film made of flexible epoxy resin - glass cloth or flexiblepolyamide - paper. Furthermore, a variety of above-described insulatinglaminated plates, sheets or films with an aluminum plate or iron plateconnected (to the surface of the unit opposite to the surface where theresistor pattern film is formed) can be employed.

Inorganic materials such as ceramic plates, and glass plates in whichresins and rubbers such as epoxy resin, polyester, polyurethane,polyamideimide, polyimide and rubber are employed as adhesive layers,can also be employed as the insulating support.

For simplification in description, the structure of the printed circuitsubstrate in which the high conductive material layer on which theresistor pattern film and the conductor pattern film are formed in thepredetermined positional relation to each other is combined with onlyone surface of the insulating support has been described. However, itshould be noted that the printed circuit substrate includes a structurein which the high conductive material layers having the resistor patternfilms and the conductor pattern films are provided on the two oppositesurfaces of the insulating support, respectively, and a structure inwhich the high conductive material layer having the resistor patternfilm and the conductor pattern film is provided on one of the twoopposite surfaces of the insulating support while the high conductivematerial layer without such pattern films (for forming conductors orelectrodes by etching) is provided on the other surface of theinsulating support.

In the former structure where two high conductive material layers withthe pattern films are provided on both sides of the insulating support,it is advisable that, when the insulating support is combined, guideholes are formed in the corners of the two high conductive materiallayers in advance so that the insulating support is combined with thehigh conductive material layers by fixing them in place with guide pins.

Well known etching solutions can be employed as the etching solution forthe high conductive material layer. For instance, in the case of copperfoils, one selected out of the group consisting of ferric chloride,ammonium persulfate, cupric chloride, a chromic acid sulfuric acidmixture solution, and a variety of ammoniachelate-type etching solutionis employed by taking into consideration the corrosion resistance of thematerial of the resistor pattern film.

As is apparent from the above description, the printed circuit substratewith the resistor according to the invention has a considerably usefulmerit that it can be conversed into a printed circuit board with highaccuracy by a simple process. The importance features of the presentinvention are as follows:

(1) In the case of the conventional printed circuit substrate whosestructure is such that a resistance layer is provided on the entiresurface of a high conductive material layer such as a copper foil and aninsulating support is combined with the side of the resistance layer,the high conductive material layer is subjected to two etchingprocesses, and the resistance layer is subjected to one etching process.Accordingly, the resistance region of the resultant printed circuitboard is subjected to the etching process three times; that is, it isexcessively etched, which leads to a decrease in etching accuracy.Furthermore, the conventional printed circuit substrate necessitates aphoto-masking process following the etching process, the photo-maskingprocess including photoresist coating, exposing and developingprocesses, as a result of which the auxiliary material cost and themanufacturing cost are necessarily increased, and the yield inmanufacturing of the desired printed circuit board is lowered.

On the other hand, according to the invention, the conductor patternfilm is formed on one surface of the high conductive material layerforming the circuit substrate, while the resistor pattern film is formedon the other surface. Therefore, by employing a material which isanti-corrosive against the etching solution applied to the highconductive material layer, as the conductor pattern film, the desiredprinted circuit board with resistance elements can be formed by carryingout the etching process for the high conductive material layer onlyonce. Accordingly, it is possible to reduce the number of etchingprocesses to one-third of that in the case of conventional printedcircuit substrate. This is one of the significant merits of theinvention. Since it is not necessary to subject the resistor patternfilm to etching, it goes without saying that the resistor pattern filmdoes not suffer from excessive etching.

Furthermore, the photo-masking process is carried out only inmanufacturing the circuit substrate, and is not needed in treatmentprocess. Therefore, the manufacuturer can save the equipment cost,auxiliary material cost and matching cost which is necessary for thephoto-masking process, and the yield of manufacturing the printedcircuit board can be improved.

(2) In the conventional printed circuit substrate, the resistance layeris formed on the entire surface of the high conductive material layer,and therefore it is necessary to etch the resistance layer in order toform the required pattern. Accordingly, the material of the resitancelayer is limited to, for instance, the alloy of nickel and phosphoruswhich can be etched, no matter how excellent other materials are incharacteristic. That is, a number of noble metals which cannot be etchedor anti-corrosive alloys cannot be employed as the resistance layer.

On the other hand, in the present invention, the resistor pattern filmis not subjected to etching. Accordingly, anti-corrosive metallicmaterials can be employed, which contributes to improvement of stabilityand performance of the resistance elements.

(3) In general, an actual printed circuit board with resistors needs avariety of resistors different in resistance. However, in the prior art,the resistance layer is formed on the entire surface of the highconductive material layer, and therefore only one kind of resistancelayer is necessarily employed. Accordingly, the sheet resistance valueis also limited to one kind. Thus, the conventional printed circuitboard is limited in resistance value.

On the other hand, according to the invention, the above-describeddrawback accompanying the conventional printed circuit board can becompletely eliminated. In other words, if the photo-masking process andthe formation of the resistor pattern film for the high conductivematerial layer are repeated twice or more, more than two kinds ofresistor pattern film different in sheet resistance can be incorporatedin the printed circuit substrate, whereby the resistance range of theresistance elements can be increased.

(4) In the prior art, formation of the resistance pattern from theresistance layer is carried out by etching a thick high-conductivematerial layer (for instance 35μ in the case of a copper foil which ismost extensively employed) through a photo-mask. Therefore, it isimpossible to manufacture resistance elements in the form of a fine,delicate pattern.

On the other hand, in the circuit substrate according to the inventionthe resistor pattern film is formed directly on the high conductivematerial layer by plating or the like. Therefore, it is possible tobuild in the circuit substrate resistance elements in the form of afine, delicate pattern. In addition, even if the same material as thatin the prior art is used, it is possible to manufacture resistanceelemetns higher in resistance.

(5) In the prior art, the resistance layer is formed over the entiresurface of the high conductive material layer by plating. On the otherhand, in the invention, plating the resistor pattern film is effected inthe form of a pattern. Therefore, consumption of the plating bath isgreatly reduced, and the plating bath can be maintained stable for along period of time, which leads to reducing cost and to savingmaterial.

Now, this invention will be described concretely with reference toexamples thereof.

EXAMPLE 1

A copper foil having a particular size is cut, and it is immersed in acleaning solution (obtained by diluting one volume of condensate ofShiply Company Inc. Neutra-Clean 68 with one volume of water, at 40° C.)for three minutes. Thereafter, the copper foil thus treated is rinsed.Then, it is immersed in 10% sulfuric acid for three minutes. Thereafter,it is rinsed and dried.

The copper foil thus treated is immersed in a liquid-state photoresist(which is a photoresist AZ-111 made by the Shiply Company Inc.), and isthen dried by the ordingary method to cover the two surfaces of thecopper foil with the photoresist. Then, the copper foil with thephotoresist is placed between the photographic negative for resistorpattern and the photographic negative for cunductor (includingelectrodes) pattern which have been provided in advance as shown in FIG.7, and is subjected to exposure by means of a double surface exposeraccording to the ordinary method. Then, it is developed with a specificdeveloping solution, thereby exposing the surfaces of the copper foil incorrespondence to the resistor pattern and the conductor pattern.Thereafter, it is rinsed, and is then immersed in the above-describedcleaning solution (Neutra-Clean 68) for three minutes. Furthermore, itis rinsed and is then immersed in 20% hydrochloric acid for threeminutes. Thereafter, it is rinsed and is then cleaned with a deionizedwater.

Then, the copper foil is subjected to tin-nickel plating to formtin-nickel films on the copper-exposed surfaces of the copper foil, thatis, to form a resistor pattern film and a conductor pattern film.

    ______________________________________                                        Composition of Plating Bath                                                   ______________________________________                                        SnC1.sub.2 2H.sub.2 O  28 g/l                                                 NiCl.sub.2 6H.sub.2 O  30 g/l                                                 K.sub.4 P.sub.2 O.sub.7 3H.sub.2 O                                                                  200 g/l                                                 Nitroethane            20 g/l                                                 Diammonium citrate     10 g/l                                                 Electrolytic Conditions                                                       Temperature           50° C.                                           PH                    8.2 (25° C.)                                     Current density       0.1 A/dm.sup.2                                          Agitation             None                                                    Anode                 Nickel Plate                                            ______________________________________                                    

A resistance film of a sheet resistance 300 Ω/□ can be obtained bysubjecting the copper foil to plating for 70 seconds. After theelectrodeposition, the copper foil is taken out, and the photoresistleft on the copper foil is removed by the ordinary method. Then, it isrinsed with hot water, and thereafter it is rinsed with a deionizedwater is dried.

Then, an epoxy resin containing glass cloth (so-called prepreg) isplaced over the surface of the copper foil where the resistor patternfilm have been formed, and is then heated and pressurized by means of alamination press so that the glass cloth is combined with the copperfoil in the form of a laminated plate. Thus, the printed circuitsubstrate with the resistance elements according to the invention hasbeen obtained.

A printed circuit board with resistance elements is fabricated from theprinted circuit substrate as follows:

The copper of the substrate is subjected to etching by using Neutra-EtchV-l (made by Shiply Company Inc.). The temperature of the etchingsolution is 52° C., and the PH thereof is 7.5 (at 25° C.).

The conductor (including electrodes) section is protected by theaforementioned tin-nickel film. The copper is etched, as a result ofwhich the tin-nickel pattern film serving as the resistance elements isexposed.

After cleaning it is dried. Then, a solder stock-off is applied to theresistance region by printing, and is then heated. Thus, the printedcircuit board with resistance elements has been fabricated.

The characteristics of the resistance element is as indicated below:

Sheet resistance value: 300 Ω/□ (variation within 5%)

Resistance-temperature coefficient: +70 ppm/°C. or less (Temperaturerange -65° to +125° C.)

Moisture-proof characteristic: +0.7 or less

(Resistance variation percentage in 240 hours with a temberature of 40°C., a relative humidity 95%, and no-load)

Heat-resisting characteristic in soldering: +0.7% or less

(Resistance variation percentage after it is immersed in a solderingbath at a temperature of 260° C. for 20 seconds)

EXAMPLE 2

A printed circuit substrate including resistor pattern films differentin sheet resistance is manufactured and the circuit board withresistance elements is treated as follows:

Similarly as in the case of Example 1, a copper foil subjected toplating is taken out of a plating bath, and is then rinsed. Thereafter,the photoresist is removed therefrom by the ordinary method, and is thensubjected to rinsing and drying. Then, similarly as in theabove-described method, photoresist is applied to the unit and is driedagain.

Then the unit is subjected to exposure through the second photographicnegative for resistor pattern which has been prepared in advance, and isdeveloped with a specific developing solution to expose the surfaces ofthe copper foil in the form of a resistor pattern and at desiredpositions. The unit thus treated is rinsed and is then cleaned with adeionized water. Thereafter, the second plating is carried out with theplating bath described in Example 1.

A resistance film having a sheet resistance of 100 Ω/ is obtained underthe conditions that the current density is 0.1 A/cm² and the platingperiod of time is 180 seconds.

After plating, the unit is sufficiently rinsed, and the photoresist leftis removed. Thereafter, the unit is rinsed with hot water, and is thencleaned with a deionized water. Furthermore, it is dried. Then,similarly as in the case of Example 1, the insulating support iscombined with the unit thus treated. As a result, the circuit substratewith resistance elements in which two resistor pattern films, 100 Ω/□and 300 Ω/□ in sheet resistance, have been formed is obtained.Furthermore, similarly as in the above-described case, the copper isetched, and cover-coating for the resistance regions is carried out toaccomplish the formation of the circuit board with resistance elements.

The characteristics of the resistance element having a sheet resistanceof 300 Ω/□ are the same as those described above. The characteristics ofthe resistance element obtained by applying the second plating are asfollows:

Sheet resistance value: 100 Ω/□ (variation ±5% or less)

Resistance-temperature coefficient: +60 ppm/°C. or less (Temperaturerange -65° to +125° C.)

Moisture-proof characteristic: +0.4% or less

(Resistance variation percentage in 240 hours with a temperature of 40°C., a relative humidity 95%, and no-load).

Heat-resisting characteristic in soldering: +0.3% or less

(Resistance variation percentage after it is immersed in a solderingbath at a temperature of 260° C. for 20 seconds)

EXAMPLE 3

A printed circuit substrate having resistance elements, whose conductor(including electrodes) section surface is plated with gold, ismanufactured as follows:

Tin-nickel patterns are formed on both surfaces of a copper foil bytin-nickel plating. The unit thus formed is subjected to rinsing anddrying. Thereafter, without removal of the left photoresist, a maskingadhesive sheet (SPV No. 224 made by the Nitto Denki Kogyo K.K.) isfixedly placed over the surface of the unit where the resistor patternfilm has been formed. Then, the unit thus treated is immersed in acleaning solution (which is the aforementioned Neutra-clean 68) forthree minutes. After being rinsed, the unit is immersed in surfacesmoothening solution (Japan Metal Finishing Company Limited EnplalateAD-485) for 30 seconds, and is then rinsed. Furthermore, it is immersedin 10% sulfuric acid for 30 seconds, and is then rinsed. Thereafter, itis rinsed with a deionized water, and is then subjected to gold platingunder the following conditions:

Plating bath: Temperex 401

(made by the Nippon Electroplating Engineers K.K.)

Electrolytic conditions

Temperature: 57° C.

PH: 6.0 (25° C.)

Current density: 0.5 A/dm²

Agitation: effected

Anode: insoluble

After completion of the gold plating, the unit is rinsed thoroughly, andthe masking sheet and the left photoresist are removed in the ordinarymethod. Then, the unit is rinsed thoroughly again and is then dried.Thereafter, an insulating support is combined with the surface of theunit where the resistor pattern film has been formed. Thus, a printedcircuit substrate with resistance elements in which the conductorpattern film is plated with gold is obtained. This printed circuitsubstrate can be converted into a circuit board with resistance elementsin accordance with the same process as that in Example 1.

EXAMPLE 4

Similarly as in the case of Example 1, a copper foil (covered withphotoresist except for the resistor and conductor pattern sections) thesurface of which is exposed in the form of a resistor pattern and in theform of a conductor (including electrodes) pattern is cleaned with acleaning solution (Neutra-clean 68 made by Shiply Company Inc.) and 20%hydrochloric acid. Thereafter, the unit is subjected to rinsing, and isthen cleaned with a deionized water. Then, the copper exposed portionsof the unit are subjected to plating under the following conditions:

    ______________________________________                                        Composition of Plating Bath                                                   KAu (CN).sub.2          17.5 g/l                                              Potassium citrate (K.sub.3 C.sub.6 H.sub.5 O.sub.7 H.sub.2 O)                                         70 g/l                                                Citric acid             18 g/l                                                Electrolytic conditions                                                       Temperature: 55° C.                                                    PH: 6.0 (25° C.)                                                       Current density: 0.03 A/dm.sup.2                                              Agitation: Effected                                                           Anode: Platinum plated titanium net                                           Plating period: 150 seconds                                                   ______________________________________                                    

After completion of the plating process, similarly as in the case ofExample 1 a printed circuit substrate with resistance elements isobtained. Furthermore, the printed circuit substrate is converted into acircuit board with resistance elements in the same manner as thatdescribed above.

In this example also, the gold plating film serves not only as theresistor pattern film but also as a etch-resist for protecting theconductor (including electrodes) section.

Thus, it is apparent that the gold plating film which has beenunemployable as the resistance film in the conventional method becauseof difficulty in etching it becomes employable according to theinvention. The characteristics of the obtained circuit board are aslisted below:

(Characteristics)

Sheet resistance: 200 Ω/□ (variation ±5% or less)

Resistance-temperature coefficient: +70 ppm/°C. or less (Temperaturerange -65° to +125° C.)

Moisture-proof characteristic: +0.5% ot less

(Resistance variation percentage in 240 hours with a temperature of 40°C., a relative humidity 95%, and no-load)

Heat-resisting characteristic in soldering: +0.7% or less

(Resistance variation percentage after it is immersed in a solderingbath at a temperature of 260° C. for 20 seconds)

What is claimed is:
 1. A printed substrate incorporating resistiveelements comprising in combination:(a) an insulating support; (b) alayer of resistive material of predetermined dimensions embedded in saidinsulating support and having an outer surface flush with an outersurface of said insulating support; (c) first and second regions ofhighly conductive material positioned in contact with spaced-apartportions of said layer of resistive material, said first and secondregions of highly conductive material being positioned upon at leastportions of said outer surface of said resistive layer; and (d) firstand second conductor pattern film layers formed on said first and secondregions of highly conductive material respectively at a positionopposite said layer of resistive material.
 2. A printed circuitsubstrate with resistance elements as claimed in claim 1, wherein saidfirst and second regions of highly conductive material are positionedboth upon portions of said outer surface of said resistive layer andportions of said outer surface of said insulating support.
 3. A printedcircuit substrate with resistance elements as claimed in claim 1, inwhich said conductor pattern film layers are made of a metallic materialwhich is anti-corrosive against an etching solution for etching thematerial of said regions of highly conductive material.
 4. A printedcircuit substrate with resistance elements as claimed in claim 1, inwhich said layer of resistive material and conductor pattern film layersare made of the same anti-corrosive metallic material which isanti-corrosive against an etching solution for etching the material ofsaid regions of highly conductive material.
 5. A printed circuitsubstrate with resistance elements as claimed in claim 1, in which saidlayer of resistive material and conductor pattern film layers are madeof different anti-corrosive metallic materials each of which isanti-corrosive against an etching solution for etching the material ofsaid regions of highly conductive material.
 6. A printed circuitsubstrate with resistance elements as claimed in claim 1, in which saidlayer of resistive material and conductor pattern film layers are formedby plating.
 7. A printed circuit substrate with resistance elements asclaimed in claim 1, in which said layer of resistive material is formedby printing a resistance material, while said conductor pattern filmlayers are formed by plating with a metallic material which isanti-corrosive against an etching solution for etching the material ofsaid regions of highly conductive material.